If one read the “fine print” from the CDC and the manufacturers when they announce the vaccine, you would have known that they never claimed it would make you immune from Covid19, not would it prevent vaccinated people from spreading. They claimed only that it would the chance of a vaccinated individual becoming seriously ill (which combined with the fact the very few people who get Covid19 actually become seriously ill to begin with, would make a vaccinated individual would be very unlikely to become severely ill).
The politicians, mass media (including social media), and people who “talking points” rather than long articles to read, ERRONEOUSLY assumed the vaccinated for Covid19 was like more familiar vaccine (total immunity including being unable to spread the disease).